Cascading Style Sheets (CSS) are the modern standard for website presentation. When combined with structural markup language like HTML, XHTML, or XML (though not limited to these), CSS provide Internet browsers with the information that enables them to present all the visual aspects and elements of a web document. CSS apply things like borders, spacing between paragraphs, margins, headings on images, control of font faces or colors, background colors and images, textual effects like underlined or strike-through text, layering, positioning, and a number of other presentational effects. CSS controls the presentational aspects of a web page’s design, whereas HTML, XHTML, or XML control the
structure of a webpage, which means more than determining that certain text is a heading, other text is a paragraph, other text os a list of hyperlinks, and so on.
By using modern standards like CSS and XHTML, you can dramatically reduce the cost of building and maintaining a website when compared to legacy HTML-only pages. You can also greatly reduce the amount of physical bandwidth and hard disk space required, resulting in immediate long-term benefits for any webmasters and web visitor